Congratulations. You have money, a family, a large house, success. You have achieved all the goals you set for yourself after college.

Now what?

Yes, it's true that F. Scott Fitzgerald once wrote that "there are no second acts in American lives," but what did he know? He was a drunk who died at the age of 45. If he had been able to lay off the sauce and spend more time at the gym, he may have instead gone on to write a few more great novels.

The point is that there are second acts in American lives — but only if one has enough determination to make them happen. For some people, that second act might take the form of writing a book, charitable work or, as is the case with New York's billionaire mayor Michael Bloomberg, politics. Other people just buy a red sports car or a sailboat.

For many others, however, the second act is often athletic, partly because the goals are easily defined. Running a marathon or climbing a mountain is a straightforward, if not challenging, objective. No special skills are required, nor are there any illusions about, say, ditching your current job to become a professional triathlete. All that is required is preparation and dedication.

But the appeal of athletic challenge is possibly even more compelling after college than when one is in school. After all, sports are a big part of education, but most people lose that outlet in the real world. Going to the gym just isn't the same thing. It is the absence of this competition, as well as the inevitable softening of the belly and slackening of the muscles, that can often serve to inspire potential second-actors to tackle challenges that they may have once thought beyond their abilities.

The data bears it out. According to USA Triathlon, for example, the two demographics with the largest participation are ages between 30 and 39 at 38 percent, and between 40 and 49 with 28 percent.

"It's nice to have activities that make a person feel satisfaction. It makes life interesting and meaningful," says Dr. Ravi Amin, who is associate chair of psychiatry at Long Island College Hospital. At the age of 40, Amin took up running as a hobby and since then, has run the New York City Marathon twice. "My physical ability is about the same as when I was 25 or 26, and I feel better than I did then. When you accomplish such a goal, it leaves you with inner peace and satisfaction."

With the right motivation, a person can go a long way, literally. For example, biking across the U.S. Every summer cyclists can participate in the annual Race Across America, a 12-day race that starts in Oceanside, Calif., and ends in Atlantic City, N.J. The whole time a support crew follows the rider in a car and assists their every need. "There's a whole team dedicated to special treatment just for you. It's people giving up a week of their lives to fill your water bottles and help you out," says Paul Skilbeck from the RAAM's board.

Competing in athletic events takes not only time and dedication, but also a small investment to get started — some more than others. Training for a marathon requires a relatively small outlay for running shoes, maybe a heart-rate monitor and the costs of entrance fees. Setting your sights on climbing Mt. McKinley involves not only rigorous physical training but also the costs of travel, guide services and gear, or an expenditure of at least $8,000, and possibly considerably more.

Multisport competitions are also gaining popularity, such as the Ironman competition in the city of Kailua-Kona, Hawaii, where the largest age divisions are those with people from ages 35 to 49. This past year, the competition had its first 80-year-old finish the 2.4 mile swim, 112 mile bike ride and 26.2 mile run. To be considered an official Ironman, the event must be completed, in succession, within 17 hours.

"The best way to train for triathlons is by concentrating on your weakest point, and for most people it's swimming," says Romi F. Odeh, the owner of Formwell Personal Training in Atlanta, Ga. "We have a lot of people who are beginners, and they get started in sprint triathlons, which are a 600-meter swim, a 10- to 15-mile bike ride, and then usually a three-mile run."

But for those who just don't seek pleasure in finishing a race, there's still a way to fulfill a dream and give to a charity at the same time with the New York Yankees Fantasy Camp. For about $5,000, it's a weeklong camp held at Legends Field in Tampa, Fla., where the team has Spring Training. Campers get to use the Yankee training staff along with the clubhouse and facilities just like a real team member would. It's a week of working out Major League Baseball-style.

Remember, whichever physical challenge appeals to you, the end result is that you will find yourself in better shape and, maybe even more important, feel better about yourself. Of course, that doesn't mean you still can't go out there and buy a sports car or a sailboat.